WO1999061524A1

WO1999061524A1 - Film containing starch or starch derivatives and polyester urethanes

Info

Publication number: WO1999061524A1
Application number: PCT/EP1999/003400
Authority: WO
Inventors: Klaus-Dieter Hammer; Michael Ahlers; Gerhard Grolig; Hans-Gerhard Fritz; Thomas Seidenstücker
Original assignee: Kalle Nalo Gmbh & Co. Kg
Priority date: 1998-05-25
Filing date: 1999-05-18
Publication date: 1999-12-02
Also published as: US6821588B1; DE19822979A1; EP1102814B1; HUP0102392A2; JP2002516372A; PL344485A1; DE59908204D1; HUP0102392A3; RU2220161C2; ATE257166T1; AU4144699A; ES2212561T3; EP1102814A1

Abstract

The invention relates to a film which is produced from a thermoplastic polymer mixture containing the following: a) thermoplastic starch and/or a thermoplastic starch derivative and b) at least one polyester urethane, the weight ratio a):b) being 75:25 to 5:95 and the surface-related degree of stretching of the film being 2 to 70. The polyester urethane forms a matrix in the mixture and the thermoplastic starch or thermoplastic starch derivative becomes embedded in said matrix, said thermoplastic starch or thermoplastic starch derivative being distributed in a microdispersion in the form of particles with a diameter dp of 0.05 to 30 νm. The invention also relates to a method for the inventive film and to its use as a packaging film, especially for artificial sausage skins.

Description

FILM CONTAINING STARCH OR STARCH DERIVATIVES AND POLYESTERURETHANE

The invention relates to a film which contains thermoplastic starch and / or thermoplastic starch derivatives and is particularly suitable as a food casing. In addition, the invention relates to a method for producing this

Food casing and its use as packaging film, in particular as a sausage casing.

Most sausage casings are made from animal intestine, but also from fiber-reinforced regenerated cellulose, collagen or synthetic polymers. Cellulose and

Although collagen is of natural origin, the manufacture of such sausage casings is carried out using complex and environmentally harmful processes. In contrast, casings made of other material, for example of protein- or acrylate-coated fabric, are of little importance.

Of the known casings, those made from cellulose hydrate cover the widest range of applications. However, they have too high a permeability for water vapor and / or oxygen for some applications. Collagen casings are less permeable, but are too unstable. The casings made of synthetic polymers are unsuitable for the production of dry sausage. Although they can be produced inexpensively and easily, for example by extrusion, in contrast to the cellulose hydrate or collagen casings, they are not biodegradable.

The one described in EP-A 0 709 030, by extrusion of thermoplastic

Starch-made sausage casings are biodegradable, but still have deficits. In particular, it is not sufficiently resistant to boiling and tends to become brittle after water treatment or through loss of plasticizer.

Finally, single-layer or multilayer tubular, biaxially stretched food casings are known, which consist of a thermoplastic, biodegradable polymer or at least one layer thereof contains (EP-A 0 820 698). They are made by an extrusion process. Suitable thermoplastically processable, biodegradable polymers here are aliphatic or partially aromatic polyesters, thermoplastic aliphatic polyester urethanes, aliphatic-aromatic polyester carbonates and, in particular, aliphatic polyester amides. Tubular shells made of these

However, polymers, especially those made from polyester urethanes, show poor caliber consistency, which leads to processing problems.

The object was therefore to develop a food casing which can be produced from natural, renewable raw materials in a simple and environmentally friendly manner, if possible using an extrusion process, and which is at the same time compostable or at least biodegradable. The casing should be sufficiently permeable and for practically all types of sausage, i.e. H. can be used for the production of cooked and scalded sausages as well as raw sausages.

The object is achieved by a mixture (blend) of a) thermoplastic starch and / or a thermoplastic starch derivative (both referred to below as "TPS") and b) at least one polyester urethane.

The present application thus relates to a film which contains thermoplastic starch and / or a thermoplastic starch derivative and is characterized in that it is produced from a thermoplastic mixture which a) thermoplastic starch and / or a thermoplastic starch derivative and b) at least comprises a polyester urethane, the weight ratio a): b) being in the range from 75:25 to 5:95, preferably 30:70 to 60:40, and in that it has a degree of stretching by area of 2 to 70, preferably 4 to 40, particularly preferably 6 to 20. If necessary, the film can also contain native starch. In order to fine-tune the stress / strain curve, organic or organic, finely dispersed fillers may be added. In the polymer blend, the polyester urethane forms the continuous matrix in which the thermoplastic starch or the thermoplastic starch derivative in microdisperse distribution in the form of discrete particles with a diameter d _p of 0.05 to 30 μm, preferably between 0.1 and 3.0 μm, is embedded. The film has been stretched

State preferably a thickness of 30 to 120 μm, particularly preferably of 50 to 80 μm. It can be used as packaging film, especially for food, especially as a seamless, tubular sausage casing.

The thermoplastic starch derivative is preferably a starch ester as described in detail in DE-A 195 15477. The acid component in the ester is generally a (C ₂ -C ₁₀ ) alkanoic acid, which is preferably not or only slightly branched. A particularly preferred and inexpensive starch alkanoate is starch acetate with a degree of substitution of less than 3, in particular from 1.5 to 2.4. Unlike the starch itself, starch esters such as starch acetate are already thermoplastic as such and do not have to be plasticized first. Starch esters with a longer alkyl chain, for example starch hexanoates, octanoates or decanoates, cause a change in the suppleness and toughness as well as the permeation of the food casings. By combining different starch esters, casings with very special properties can be produced. Starch ethers and thermoplastic starch derivatives which have cationic quaternary side groups with hydrophobic (C ₂ -C ₁₈ ) alkyl groups, preferably (C ₂ -C ₁₂ ) alkyl groups, are also suitable. Finally, anionic starch derivatives can also be used.

It has been shown that casings which consist only of thermoplastic starch and / or thermoplastic starch derivatives do not yet have the desired degree of extensibility, strength, toughness, suppleness, but above all stability towards hot or boiling water. Cases made of pure polyester urethane also do not have the desired properties. In particular, they lack strength, temperature stability and constant caliber. They cannot be significantly improved even if various low-molecular substances, such as lubricants, plasticizers and fillers, are added to the thermoplastic starch or the thermoplastic starch derivative.

It has surprisingly been found that a substantial improvement occurs when the thermoplastic starch or the starch derivative is mixed with thermoplastic polyester urethanes.

The thermoplastic polyester urethane (hereinafter also referred to as "TPU") consists of hard polyurethane and soft polyester segments, the segments being arranged in an alternating sequence. Segments with a glass transition temperature (T _g ) of −20 ° C. or below are referred to as “soft”, whereas those with a T _g of + 30 ° C. or above are referred to as “hard”. The polyester urethane can be aliphatic or aromatic in nature. The proportion of the polyurethane segments in the thermoplastic polyester urethane is 10 to 90% by weight, preferably 20 to 50% by weight, in each case based on the total weight of the polyester urethane. They generally consist of diisocyanate and diol units. The diisocyanate units can be aliphatic, cycioaliphatic or aromatic. Examples of aliphatic diisocyanates are butane-1,4-diisocyanate and hexane-1,6-diisocyanate. Isophorone diisocyanate (= 3-isocyanatomethyl-3,5,5-trimethylcyclohexane isocyanate) represents a cycloaliphatic diisocyanate. Toluene-2,4- and -2,6-diisocyanate, diphenylmethane-2,2'-, -2,4'-, -2,6'- and -4,4'-diisocyanate and naphthalene-1, 5- diisocyanate are preferred aromatic diisocyanates.

The polyester segments generally have an average molecular weight M _w of 500 to 10,000 g / mol, preferably 1,000 to 4,000 g / mol. They preferably consist of units of di- or polyhydric alcohols and units of di- or polyvalent carboxylic acids. They can be prepared from the starting materials mentioned by condensation polymerization in the presence of catalysts, such as titanium butylate (= orthotitanic acid tetrabutyl ester). However, the polyester segments usually consist of diol and dicarboxylic acid units. Corresponding acid derivatives, such as carbonyl halides (in particular carbonyl chlorides), carboxylic acid anhydrides or carboxylic acid (C ₁ -C ₄ ) alkyl esters can of course also be used in the condensation reaction instead of the free acids. The diols or polyols generally have an aliphatic or cycloaliphatic backbone. Preferred diols for the production of the ester segments are ethane-1, 2-diol (= ethylene glycol), propane-1, 2- and -1, 3-diol, 2,2-

Dimethyl-propane-1, 3-diol (= neopentyl glycol), butane-1, 4-diol, pentane-1, 5-diol, hexane-1, 6-diol and cyclohexanediyl-bismethanol (especially cyclohexane-1, 4-diyl bismethanol). Mixtures of several different diols or polyols can also be used. The di- or polycarboxylic acids preferably also have an aliphatic or cycloaliphatic backbone, aliphatic dicarboxylic acids (such as succinic acid or adipic acid) being preferred. Adipic acid is particularly preferred. A dicarboxylic acid with a cycloaliphatic backbone is, for example, cyclohexanedicarboxylic acid (in particular cyclohexane-1,4-dicarboxylic acid). The polyester segments can also be constructed from units of hydroxycarboxylic acids or their derivatives, for example from 3-hydroxy-propionic acid, 3-hydroxy-butyric acid, 4-hydroxy-butyric acid, 5-hydroxy-pentanoic acid or e-caprolactone. Particularly suitable are polyester urethanes that have minutes at a temperature of 190 ° C and a load of 21 6 kg have a melt volume index MVI (determined according to ISO 01133) in the range of about 5 to 15 ^cm3 / 10 min.

The film of the invention can surprisingly be heat sealed or welded. A temperature of about 100 to 250 ° C. and a contact time of about 0.1 to 5 s are sufficient for this. There is no additional glue required. In contrast, films made from thermoplastic starch alone are not heat-sealable. The tubular food casing according to the invention is also permeable to smoke, including cold smoke. It is smooth without being greasy. Its appearance is largely like that of a natural casing. Fat particles stand out well because the shell is preferably transparent. Even after considerable water loss, it still sits smoothly and plump on the sausage meat. This effect is mainly attributed to the elastic properties of the TPU matrix. The shell can easily be peeled off without spontaneously bursting. The tear resistance is good. This property can also be changed by changing the type and proportion of

Adjust components in the thermoplastic mixture, especially by incorporating a filler (e.g. native fine grain starch), as required.

In addition to components a) and b), the thermoplastic mixture can also contain other low or high molecular weight constituents which serve in particular as plasticizers or lubricants or improve the compatibility of the components with one another. These constituents can, if appropriate, further improve or adjust the homogeneity and flowability of the extrudable thermoplastic mixture.

Particularly suitable plasticizers are mono-, di-, tri- and polyglycerol, sorbitol, polyethylene glycol (PEG), triethyl citrate, triethyl acetyl citrate, glycerol triacetate, phthalate esters (especially dimethyl phthalate, diethyl phthalate and dibutyl phthalate) and sorbitol mono- and . The proportion of plasticizer (s) is up to 40% by weight, preferably up to 25% by weight, in each case based on the total weight of the thermoplastic mixture.

Lubricants which improve the homogeneity of the thermoplastic mixture are, in particular, vegetable fats or oils, synthetic triglycerides, lecithins, ethoxylated fatty alcohols or waxes. Containing epoxy groups Oils, in particular epoxidized linseed oil, are particularly suitable additives which ensure optimum dispersion of the thermoplastic starch in the thermoplastic polyester urethane and, at the same time, surprisingly reduce the extruder torque in the course of the mixture preparation. The proportion of the lubricants is up to 12% by weight, preferably 0.1 to 6% by weight, in each case based on the total weight of the mixture.

Finally, the film according to the invention can be reinforced with fibers. In general, the fibers are relatively short (on average about 0.1 to 3 mm, preferably 0.2 to 1.5 mm). So that the casing remains biodegradable

Fibers made from cotton linters, wood pulp, from regenerated cellulose ("regenerated fibers"), from hemp, flax, sisal or jute are particularly suitable. The proportion of fibers is up to 30% by weight, based on the total weight of TPS + TPU. The fiber content is preferably 2 to 15% by weight, in each case based on the total weight of the mixture. The fibers are in the course of

Blend preparation process evenly distributed in the thermoplastic mixture.

The film can either contain fillers instead of the fibers or in addition. Calcium carbonate, talc,

Kaolin (especially kaolin / quartz mixtures, known as "Neuburg Siliceous Earth"), titanium dioxide, silicates (especially wollastonite, an inosilicate), anhydrite (= calcium sulfate), particles of cellulose or native starch (especially those with a particle diameter of 15 μm or less). The median diameter of the filler particles (d _pF ) is in the range from 0.1 to

50 μm, preferably 0.1 to 20 μm, particularly preferably 1 to 5 μm. Their proportion can be up to 30% by weight, but is preferably 2 to 15% by weight, particularly preferably 4 to 10% by weight, in each case based on the total weight of the thermoplastic mixture. For films with a particularly high stability against hot or boiling water, it has proven to be advantageous to add crosslinking agents to the thermoplastic mixture. Suitable crosslinking agents are, for example, dicarboxylic acids, di- or triisocyanates (especially hexamethylene diisocyanate), dialdehydes (especially glyoxal), diepoxides, diimines or

Silanes or siloxanes with vinyl group (s), for example vinyl-methyl-silane. The crosslinking agent is preferably only added when the other components of the mixture have already melted. The proportion of crosslinker (s) is up to 10% by weight, preferably 0.5 to 5% by weight, particularly preferably 1 to 3% by weight, in each case based on the total weight of the thermoplastic mixture.

The production of thermoplastic starch is known for example from WO 90/05161 and 90/10019. The plasticization removes the helical structure of the native starch, so that it is then in a largely amorphous state. The thermoplastic starch contains 50 to 100% by weight, preferably at least 80% by weight, of the originally used native starch in a destructured form. The degree of destructuring can be determined by image analysis of recordings which were produced with polarized light, by dynamic differential calorimetry (DSC) or by determining the

Determine X-ray scatter. The destructuring and plasticizing takes place by heating and supplying mechanical energy, for example by longer thermal treatment in a kneader or in a single or twin screw extruder. In order for the starch to melt below its decomposition temperature, additives are necessary, such as water, glycerol, propane-1,3-diol, butane

1, 4-diol, pentane-1, 5-diol, hexane-1, 6-diol, neopentyl glycol, diglycerin, N, N-dimethyl urea, sorbitol or citrate. When plasticizing with water, about 20 to 25% by weight of water, preferably about 17% by weight of water, are added, in each case based on the weight of the native starch. A mass temperature of around 100 to 130 ° C is maintained. When plasticizing with Glycerin is about 0.5 to 30 wt .-%, preferably 8 to 25 wt .-%, again each based on the weight of the native starch. In this case, a melt temperature of 150 to 170 ° C has proven to be favorable. With this treatment, the proportion of the crystalline starch can be reduced to 5% by weight or less.

The thermoplastic mixture can be produced from the components mentioned in conventional apparatus, for example in a twin-screw extruder. Particularly suitable are extruders with two co-rotating, closely intermeshing screws, the speed of which is preferably at 50 to 400 per min. lies. They show oppositely moving screw surfaces with high shear in the gap area and can therefore introduce a large amount of energy into the material to be extruded. A homogeneous, thermoplastic melt mixture is formed from the individual components at a temperature of 150 to 230 ° C, preferably from 170 to 210 ° C.

Several process variants are possible for producing the thermoplastic mixture. In the first variant, native starch is first plasticized with the aid of the destructuring aids described (in particular glycerol). The thermoplastic polyester urethane is then fed in via a so-called side feed extruder. It is mixed with the melted and degassed thermoplastic starch, the resulting mixture is then degassed again. The melt can then be extruded and, after cooling, can be converted into a storable granulate. It can just as well be fed directly to a ring nozzle by means of a melt pump and processed into a tubular food casing. In a further process variant, granulated thermoplastic starch or a granulated starch derivative serves as the starting material. After melting and degassing in the extruder, mixing with the TPU follows. In a third variant, the TPS and TPU are fed together to the extruder. Finally, the thermo- plastic polyester urethane also mixed with native starch and thus "filled". When mixing in the extruder, a sufficient proportion of the starch is already plasticized, especially if a plasticizing aid (eg glycerin) is added.

To produce a tubular film, the thermoplastic mixture is extruded through a heated ring die. The temperature in the ring die is 100 to 160 ° C and thus preferably somewhat lower than in the upstream heating zones of the compounding or plasticizing extruder (there it is generally 110 to 190 ° C).

The present invention thus also relates to a method for producing the film according to the invention, in which a tube produced by extrusion is blow-molded by being inflated with air (or another gas), the area-related degree of stretching λ _A = λ ₁ ^• λ ₂ im

Range is from 2 to 70, preferably from 4 to 40, particularly preferably from 6 to 20. The stretching rates in the tubular film blowing process are defined as follows: λ ₁ = D _S / D _D ; λ ₂ = v _s / v _D , λ ₃ = S _S / S _D , where

D _s film tube diameter,

D _D nozzle diameter, v _s hose withdrawal speed, v _D average melt exit speed from the nozzle, S _s film thickness and

S _P mean nozzle outlet gap.

For reasons of continuity, λ ₁ ^• λ ₂ ^• λ ₃ = 1 must apply, ie the area-related degree of stretching λ _A is inversely proportional to the product thickness reduction λ ₃ . If a flat film is to be produced, the polymer melt can also be extruded through a slot die. The specified area-related degrees of stretching can then be achieved by stretching in the longitudinal and transverse directions (for example with the aid of a tenter frame). In addition, the blow-molded tubular film described can of course also become a flat film by simply cutting it open.

Only through the stretching and orientation process do the hoses obtain the optimum strength, elongation, caliber maintenance and shrinkability. How strong each of these properties is depends primarily on the composition of the thermoplastic mixture. For example, the food casings can be adapted to the different requirements by specifically selecting the type and proportion of the individual components of the thermoplastic mixture or by adjusting the drawing parameters. If necessary, the blow-molded sleeves can also be partially heat-set. The film according to the invention generally consists of only one layer. However, multi-layer casings can also be produced by coextrusion.

By washing in a suitable bath, for example a water bath or a bath of dilute (about 1% by weight) acid, water-soluble plasticizers or plasticizing aids can be removed from the film according to the invention. Surprisingly, it was found that the mechanical properties of the film did not deteriorate as a result. The proportion of plasticizers or plasticizing agents n after this washing is preferably less than 2% by weight, based on the total weight of the dry casing.

In a further process step, the tubular casings can be provided with an inner and / or outer preparation in order to make them even more suitable for the various uses as a sausage casing. For this purpose, most of the liquid preparations, which are also customary for the finishing of cellulose hydrate casings, can be used in a correspondingly adjusted concentration. It is particularly favorable, for example, to coat the inner surface of a casing intended for permanent sausage with protein (preferably casein, gelatin, soy protein or wheat protein). The protein is usually bound to the surface of the shell with a (di) aldehyde. The peelability of the sausage casing can be adjusted by using resins or by adding release agents to the protein / aldehyde. The adhesion of the casing to the sausage meat can be reduced to a strong separation effect using known recipes (this is necessary, for example, in the case of

Thuringian blood sausage).

Suitable external preparations are also already known from cellulose casings. By treating the outer surface of the casing with such a preparation, mold resistance, surface roughness and printability can be set in particular.

The properties of the food casing according to the invention can be varied to such an extent that it corresponds to a natural casing or a cellulose casing. Their good swelling and shrinking properties ensure that they are tightly attached to the sausage meat at all times and that no wrinkles form even when they dry slowly. The permeability of the shell for water, water vapor and oxygen can be set precisely by the choice of components. Surprisingly, it was found that the casing according to the invention is permeable to smoke, so that it is suitable for smoked raw sausage types (for example salami or

Cervelatwurst) is particularly suitable. However, other foodstuffs can also be packaged with the casing according to the invention, for example cheese.

The starch used to manufacture the casing is also one of the most popular renewable raw materials. When composting tion, the casing according to the invention is broken down particularly quickly, since the microbes, in addition to the polyester urethane, also have the easily usable starch as a carbon source. There is therefore a co-metabolic degradation in which the hard aromatic polyurethane segments are degraded much more quickly than normal.

The following examples are intended to explain the invention in more detail. The percentages are to be understood as percentages by weight, unless stated otherwise.

Production of thermoplastic polymer mixtures

example 1

Production of thermoplastic starch and the mixture of thermoplastic

Starch and polyurethane

a) 100 kg of corn starch were dried under reduced pressure to a water content of less than 0.3% in a vacuum and melted with 20 kg of glycerol (99%) and 2 kg of epoxidized linseed oil in a twin-screw extruder at 160 to 190 ° C and mixed well. It was then extruded and granulated. When storing the

Granules remained the starch in the amorphous and thus thermoplastic state.

b) 100 kg of native corn starch and 20 kg of glycerol were mixed together with 2 kg of epoxidized linseed oil in a co-rotating twin-screw extruder with a process length of 40 D and plasticized, with a starch restructuring occurring. The water content was reduced to below 1% by weight, based on the total weight of the corn starch used, by means of several degassings. The extrusion was carried out with the temperature profile 100 ° C → 175 ° C → 170 ° C. c) 60 kg of the granules described under b) were melted in a twin-screw extruder, degassed and then mixed with 60 kg of thermoplastic polyester urethane, the TPU being fed in via a side-stream extruder. The ester segments in the polyester urethane consisted of adipic acid and ethylene glycol units and had an average molar mass M _w of 3,500 to 4,000 g / mol. The thermoplastic polymer mixture was then granulated.

Example 2 Example 1 was repeated with the only difference that a polyester urethane was used, the ester segments of which were composed of adipic acid and butane 1,4-diol units and had an average molecular weight of 2,000 g / mol.

Example 3

Example 1 was repeated with the only difference that the TPU had a proportion of 40 instead of 50% by weight, based on the total weight of the thermoplastic mixture.

Example 4

Example 2 was repeated with the only difference that the TPU had a proportion of 40 instead of 50% by weight, based on the total weight of the thermoplastic mixture.

Manufacture of food casings

Example 5

The granules described in Example 2 were melted in an extruder at 170 ° C. The speed of the extruder screw was 35 revolutions per minute. The melt was then passed through a ring nozzle with a Diameter of 25 mm and a die gap of 1.0 mm extruded. The temperature in the ring nozzle was 165 ° C. and the take-off speed was 4.7 m / min. After blow molding, a tube with a diameter of 65 mm (= caliber 65) was obtained (→ D _S / D _D = λ ₁ = 2.6).

Example 6

The granules described in Example 1 were melted and extruded as in the previous example. The ring nozzle had a diameter of 25 mm and a nozzle gap of 0.75 mm. After blow molding, a tube of caliber 120 with a wall thickness of 60 μm was obtained. In the watered state, the tear strength σ _{R of} the hose was 14.3 N / mm ² and the elongation at break e _R 211%.

Example 7 The granules described in Example 2 were melted and extruded.

The ring nozzle had a diameter of 10 mm and a nozzle gap of 0.9 mm. The temperature of the tube extrusion tool was 145 ° C, the withdrawal speed 4.5 m / min. After blow molding, a tube of caliber 30 with a wall thickness of 65 μm was obtained. In the watered state, its tensile strength was 11.3 N / mm ² and that

Elongation at break at 236%.

Examples 8-10

The granules described in Example 2 were melted (melting temperature of 182 ° C.) and extruded. The screw speed of the extruder was 29 rpm. The ring nozzle had a diameter of 15 mm and a nozzle gap of 0.6 mm. The extrusion was carried out with the following cylinder temperature profile: 130 ° C, 170 ° C, 190 ° C, 190 ° C. The exit speed was 1.24 m / min, the output 2.5 kg / h. In this way, blown film tubes of caliber 45 (flat width 70 mm) with different wall thicknesses were made manufactured. The fluctuation in the flat width was ± 0.5 mm. The test data and process parameters are summarized in the following table.

table

The food casings according to the invention are stable in water, but swell therein and shrink again on drying. They can be placed on the filling device in the form of sections tied on one side or in an increased form as so-called "beads". They are particularly suitable as casings for dry sausages (ie for raw sausages with a particularly high degree of maturity).

The casings were filled with salami meat. The adhesion to the sausage meat was low (peelability after 2 weeks: "2" on a scale from 1 to 6, "1" for "very easy to peel" and "6" for "excessively strong adhesion, the casing cannot be removed without being destroyed" stands).

The advantage of the casings according to the invention is that TPU itself does not ensure a great affinity for the sausage meat and no additional preparation is required for this meat.

Claims

claims

1. Film containing thermoplastic starch and / or a thermoplastic starch derivative, characterized in that it is made from a thermoplastic mixture comprising a) thermoplastic starch and / or a thermoplastic starch derivative and b) at least one polyester urethane, the weight ratio a ): b) is in the range from 75: 25 to 5: 95, and that it has an area-related degree of stretching from 2 to 70.

2. Film according to claim 1, characterized in that the weight ratio a): b) is in the range from 30:70 to 60:40.

3. Film according to claim 1 or 2, characterized in that the thermoplastic starch derivative is a starch ester, preferably a starch alkanoate, particularly preferably starch acetate.

4. Film according to one or more of claims 1 to 3, characterized in that the polyester urethane consists of hard polyurethane and soft polyester segments, the segments being arranged in an alternating sequence.

5. Film according to claim 4, characterized in that the proportion of the polyurethane segments in the thermoplastic polyester urethane 10 to 90 wt .-%, preferably 20 to 50 wt .-%, each based on the

Total weight of polyester urethane.

6. Film according to one or more of claims 1 to 5, characterized in that the thermoplastic mixture at least one plasticizer, preferably glycerol, diglycerol, sorbitol, polyethylene Glycol, triethyl citrate, triethyl acetyl citrate, glycerol triacetate, a phthalate or sorbitol mono- or diester, the proportion of plasticizer (s) up to 40 wt .-%, preferably up to 25 wt .-%, each based on the total weight of the thermoplastic mixture.

7. Film according to one or more of claims 1 to 6, characterized in that the thermoplastic mixture contains at least one lubricant, preferably a vegetable fat or a vegetable oil, a synthetic triglyceride, lecithin, an ethoxylated fatty alcohol or a wax, the The proportion of lubricant (s) is up to 12% by weight, preferably 0.1 to 6% by weight, particularly preferably 0.2 to 6% by weight, in each case based on the total weight of the thermoplastic mixture.

8. Film according to one or more of claims 1 to 7, characterized in that the thermoplastic mixture with fibers, preferably fibers made of cotton linters, wood pulp, regenerated cellulose, hemp, flax, sisal or jute, is mixed, the Proportion of fibers up to 30% by weight, preferably 2 to 15, particularly preferably 5 to

15% by weight, based in each case on the total weight of the mixture.

9. A film according to one or more of claims 1 to 8, characterized in that the thermoplastic mixture, preferably fillers

Contains calcium carbonate, talc, kaolin, titanium dioxide, anhydrite, a silicate or fine-grained cellulose or starch particles, the proportion of the fillers up to 30% by weight, preferably 2 to 15% by weight, particularly preferably 4 to 10% by weight. %, each based on the total weight of the mixture.

10. Film according to one or more of claims 1 to 9, characterized in that the thermoplastic mixture at least one crosslinking agent, preferably a dicarboxylic acid, a di- or triisocyanate, a dialdehyde, a diepoxide, a diimine or a silane or siloxane with a vinyl group (s), the proportion of crosslinking agent (s) up to 10% by weight, preferably 0.5 to 5% by weight, particularly preferably 1 to 3% by weight, in each case based on the total weight of the mixture , is.

11. Film according to one or more of claims 1 to 10, characterized in that it is heat sealable.

12. Film according to one or more of claims 1 to 11, characterized in that it is provided with an inner and / or outer preparation.

13. A process for producing a film according to one or more of claims 1 to 12, characterized in that the tube produced from the thermoplastic mixture by extrusion is blow-molded, the area-related degree of stretching being in the range from 2 to 70, preferably from 4 to 40, particularly preferably from 6 to 20.

14. Use of the film according to one or more of claims 1 to 12 as packaging film, in particular for food, preferably as a seamless, tubular sausage casing.